Coastal dunes play a critical role in protecting communities from storms, waves, and coastal flooding. Understanding how these dunes grow and erode helps scientists improve hazard forecasts and eventually coastal resilience. By understanding coastal sand dunes, scientists can optimize nature-based defenses and guide effective restoration for stronger protections of coastal communities. Selwyn Heminway, a Hub and OSU graduate student, newly assessed the drivers of alongshore varying long-term dune change to better understand the influences of environmental and geologic factors for the overarching goal of disaster preparedness and hazard mitigation. 

The study examined 20 beach and dune transects on the Long Beach Peninsula in southwest Washington, where dunes vary in shape and size from south to north. Previous research has found that coastal dune shapes vary in nature due to a complicated relationship between dune-building and dune-erosion process. Because many environmental factors influence these processes simultaneously, it has been difficult to determine which ones matter most. In this research, Heminway analyzed a long-term dataset of beach and dune morphology from Long Beach Peninsula, Washington and tested different drivers of dune growth in a dune evolution model. This work builds on preexisting knowledge about decadal-scale dune change.

The researchers analyzed nearly three decades of shoreline and dune measurements of seasonal beach and dune profiles at 20 different transects from 1997-2023, about 2,000 total profiles, collected through the Washington State Department of Ecology’s Coastal Monitoring and Analysis Program (CMAP). From these profiles, key measurements of the beach and dune were collected, such as the shoreline change rate, beach width, dune volume, etc. Using this long-term data, researchers implemented the Dune Response Tool (DRT) to test how different environmental, geologic and beach characteristics influence dune evolution. Results from this study are understood in two forms, the quantification of alongshore variation of dune change and the model test results.

The analysis found that the rate of change and type of dune evolution varies both spatially and temporally. The researchers found that shoreline change rate—a measure of whether the shoreline is advancing or retreating—was the strongest predictor of dune growth. The model sensitivity tests supported this conclusion. Sensitivity tests with the Dune Response Tool produced the same overall trends observed in the field, strengthening the conclusion that shoreline evolution plays a primary role in controlling dune growth. This is significant because it suggests shoreline change rate is a good proxy for understanding sediment supply and dune variability, especially on Pacific Northwest beaches. Additionally, the strong relationship between shoreline advance and dune growth, suggests that prograding shorelines tend to support long-term dune development. 

The takeaway from this research is that shoreline evolution and beach morphology are the primary controls on long-term dune growth along the Long Beach Peninsula, while sediment grain size and wave collision frequency modify but do not dominate that response. 

When asked how this study improves hazard mitigation and risk management, researcher Selwyn Heminway had the following to say; 

“We can’t predict how our coastline will evolve into the future without understanding how it changed in the past. By studying this unique dataset of almost 30 years of seasonal profiles, we can get a picture of how these dunes have historically evolved and try to understand the key drivers of historical change. This knowledge can help to assess future dune vulnerability, targeted management decisions, and improve numerical models that can inform how dunes may evolve into the future, especially under changing environmental conditions.”

For more information see here.